Inventory
Lightspeed work orders have a very specific behavior when it comes to inventory management:
As soon as an inventoried item is added to a work order, the corresponding inventory is immediately removed (thus reserving the product)
As a consequence, when invoicing a work order, QuoteMachine no longer has to remove inventory at the time the invoice is created. To prevent affecting the inventory, the invoice generated by QuoteMachine is composed of miscellaneous non-inventoried items having the same name and price as the ones that were added to the work order.
Costs
When the work order is invoiced in QuoteMachine, the work order total is modified to indicate there is no remaining balance left to pay on the work order (the balance is born by the QuoteMachine invoice).
The work order balance is modified by the addition of a line with a negative amount.
To ensure the overall profit margin is correct despite the duplication of items between the Lightspeed Work Order and the QuoteMachine invoice:
Line items on the QuoteMachine Invoice have a $0 cost.
Line items on the Lightspeed work order bear the actual product cost.
Sales tax
Even if a Lightspeed work order invoiced with QuoteMachine has its total balance set to zero. Lightspeed will still account for sales tax at the line item level if your account is configured to apply a sales tax in Lightspeed's work orders.
Bear that in mind when looking at your reporting from Lightspeed as you will have the sales tax coming from both QuoteMachine and Lightspeed for a given work order.
To easily identify the sales tax volume from invoiced work-orders, you can export invoices from QuoteMachine and filter the exported CVS in your preferred spreadsheet software to only include the lines that have "external_order_id" set since this field references the Lightspeed Work order number.
Checking out work orders
Checking out work orders, even if they show a $0 total is useful as it will flag the inventoried items as sold and will update the reports accordingly in Lightspeed.
Recommended Alternatives
Invoicing Lightspeed work orders with QuoteMachine creates lots of entries in Lightspeed which does not always "feel natural" when looking at reports. QuoteMachine operates this way according to Lightspeed's Application Programming Interface (API).
Depending on your needs QuoteMachine's sales order feature could be a good replacement. It offers a cleaner, flexible workflow, fully integrated with Lightspeed Retail.